black bears and brown bears

A member of our collaborative field team watches a cliff for bear activity.

This summer my colleague Megan Owen and I were fortunate enough to have an intern working with us. Michael Forney was the John E. and Dorothy D. Helm Summer Fellow, working in our Applied Animal Ecology Division (see Summer Intern Enjoys Opportunities). He extracted behavioral data from videos of wild Andean, or spectacled, bears, living in the tropical dry forest of northwest Peru, where we work with the Spectacled Bear Conservation Society. Some of the videos were collected opportunistically by the field team, when they unexpectedly encountered a bear, and other videos were collected on a more systematic basis. There are more videos yet to review, but the preliminary results are pretty interesting.

These were the first behavioral data ever collected on wild Andean bears, and they delivered some surprises. For example, for most of the year the bears appear to lose weight, suggesting that there’s not enough food available. However, during the period of time when sapote fruit is available, the bears feed primarily on those fruits and appear to gain weight. We’d already seen this pattern, from different sources of data; however, Michael’s results suggest that dry forest Andean bears do not respond behaviorally to a feast and famine cycle like Northern Hemisphere bears would.

Sapote fruit: Does it dictate bear activity?

You may already know that American black bears and brown bears really focus on foraging during the period before they hibernate. Generally, these black and brown bears are driven to fatten up before the months when they won’t eat, so they spend as much time eating as possible. If Andean bears in the dry forest, which don’t hibernate but which do spend months with little food, behaved like these other bears, then you’d expect the bears in the videos to spend most of their time eating sapote fruit during the relatively brief period when it was available. However, Michael’s data show that adult females, with or without cubs, spend relatively little time eating, even when there appears to be a surplus of sapote fruit.

Why don’t these females spend more time feeding? We’ve generated a few hypotheses to address this question, but confirming this phenomenon and testing these hypotheses will require more data from more videos.

This is not just an abstract academic question, without relevance for the conservation of these bears. If weight gain among female Andean bears in the dry forest is constrained by sapote fruit availability, then perhaps an increase in the number of sapote trees would improve the body condition of the bears. However, if weight gain among these females is constrained by something else in addition to food availability, as might be suggested by Michael’s data, then increasing the number of sapote trees would not improve the bears’ body condition. Michael’s work reminds us that we have a lot to learn about Andean bears to further their conservation.

Unfortunately, we’ll have to pursue this question without Michael’s help, as he’s finished his internship with us and has gone south to put his talents to work in Ecuador. Thanks, Michael, and good luck!

This is a camera trap photo of the female Andean bear Magaly on December 7, 2009, when she was thin and in poor condition, before many ripe sapote fruit were available.

It was about 16 months ago when I first saw an Andean bear in the dry forest of Peru during the Southern Hemisphere winter. When I did, I was shocked. As this bear walked down the hillside toward a waterhole I could count her ribs, I could see her backbone, and I could watch her hipbones moving. Her fur was dull, and I could hardly believe how bad she looked. My colleagues had told me that the bears living in the dry forest were thin during the winter because there wasn’t much for them to eat, but I didn’t know the bears became THIN! The only other wild bear I have ever seen so scrawny was an American black bear I encountered many years ago in southwest Montana; that bear had become dependent on food it obtained from people, and it began starving when it no longer had access to the supplemental food.

This is a camera trap photo of the same female Andean bear, Magaly on April 29, 2011, after she’d become plump by feeding on sapote fruit.

When I expressed my concern over the skinniness of the dry forest bear to the field team of the Spectacled Bear Conservation Society (SBC), they told me that they had seen bears in the dry forest that looked even worse than the bear I was watching but that had nevertheless survived. In reality, I was shocked only because I didn’t have much experience in the dry forest; that bear was not unusual. She not only survived, but she mated a few months later and is now raising a young cub. Skinny dry forest bears look shocking to people who don’t have experience in the dry forest, but in fact their weight loss is part of a natural cycle that becomes obvious to anyone who studies dry forest bears for more than a year.

This is a portrait of nearly ripe sapote fruit still on the tree when there were ripe sapote fruits lying on the ground beneath the tree, and when bears were foraging on sapote fruits. We hypothesize that fruits like this one are critical for the survival of individual bears, and the bear population, in the dry forest.

Working with SBC in the dry forest, we’ve accumulated evidence over the last several years that Andean bear movements and body condition are linked to a species of tree, the sapote. Evidence from direct observations, camera traps, and satellite telemetry collars all suggests that bears focus their movements and foraging on sapote fruit when it is available, which is usually only for two to three months just before the annual rainy season.

After ripe sapote fruit become available, usually beginning in late November, the bears’ body condition improves noticeably, so that within a few weeks the bears no longer look like walking skeletons. After a few more weeks of feeding on sapote fruit, the bears start to look a little plump, although they never get as fat as American black bears and brown bears do in autumn. During the rest of the year when sapote fruit is not available, Andean bears in the dry forest gradually lose weight so that they are skinniest just before the sapote fruit is ripe. These observations strongly suggest that healthy populations of sapote trees are critical for the health of individual Andean bears in the dry forest and for the health of the dry forest bear population. The sapote tree is considered critically endangered by the Peruvian government, so we’re promoting conservation of sapote trees as part of the Andean bear conservation program.

A camera trap photo shows male Andean bear Russ on December 5, 2009, when he was thin and in poor condition before many ripe sapote fruits were available.

This is a camera trap photo of the same male Andean bear, Russ, on March 21, 2011, after he’d gained weight by feeding on sapote fruit.

The field team is seeing something unusual right now that may answer a question that’s been puzzling me for over a year. Young cubs and subadult bears often disappear when their mothers are skinniest, shortly before the sapote fruit ripens. We suspect that, unfortunately, when adult bears have a hard time finding food, many young bears do not survive. If that happens year after year, how can the population of bears in the dry forest remain stable? This year some sapote fruits are ripe earlier than normal, and some bears are starting to gain weight earlier than usual. This makes us hopeful that this year more cubs and subadult bears will survive. Of course, the survival of youngsters may depend on what the sapote trees do over the next few months, which reminds me of other questions we have. Why do sapote trees produce fruit when they do? What influences how many sapote fruits are produced? There has been a little research done on these questions, but we’ve still got some work to do to fill in the blanks!

Russ Van Horn is a scientist with the San Diego Zoo Institute for Conservation Research, leading our Andean bear conservation program. Read his previous post, Mountain Lions and Palm Trees.

I’m sometimes jealous of people who can describe how things smell, or taste. I know the same words that they do, but they truly understand how to use the words. If I could, I would describe for you what a wild Andean bear smells like. Instead, all I can say is that “Chris” smelled like a bear.

I’ve been familiar with the general smell of “bear” since I was a child, growing up in black bear country. Since then, I’ve been fortunate enough to smell black bears and brown bears across the mid-western and western United States, but this is the first time I’ve ever sniffed a wild Andean bear. Yep, Chris definitely smells like a bear!

GPS satellite radio collar, ready to be placed on Chris.

“Chris” is what the Spectacled Bear Conservation (SBC) team named this bear, but he would not respond if you were to call his name. Instead, he moves around the landscape in response to cues, signals, and motivations that we don’t yet understand. This morning, he came to the waterhole at 9:05 and turned his back on Javier Vallejos. Javier had been waiting for days for an opportunity like this and darted Chris with an injection of anesthetics. Once Chris was immobilized and his vital signs were stable, we replaced his GPS telemetry collar, gave him a thorough physical examination, and took measurements of his body.

A GPS radio collar is properly fitted to Chris’ neck.

Chris is an adult male bear, in breeding condition and in good physical condition. He’s been photographed on camera traps in the area quite often recently, so there was a good possibility that we could replace his collar, as its batteries were running low. The batteries on these collars last around 12 months, so by replacing his collar now we should be able to collect data on his movements for another year.

When he was darted last year, Chris had large blisters, or sores, on the pads of his feet. Robyn Appleton and her team can only guess that he’d worn down his footpads walking long distances on the rocky trails of the dry forest. This year, his feet are in good condition, which leads us to more questions: why were his feet more worn last year than this year; did he walk more last year than this year? If so, is this because he dispersed from his natal home range last year? Dispersal is the term for the process by which an animal relocates from one living place to another. A natal home range is the area where an animal was born. In most species of mammals, males disperse from their natal home range to a new area at around the time they go through puberty. In a few species of mammals, it is females that disperse, not males. The currently available evidence suggests that female giant pandas disperse but male giant pandas do not; male brown bears and American black bears disperse, but females of these species do not. No one has collected much evidence on whether it is male Andean bears or female Andean bears that disperse, but the probability is that males are the dispersing sex in this species. Were Chris’ blistered feet a clue as to whether male or female Andean bears disperse? Only time, and additional data collection, will answer that question.

We have additional questions on our agenda. We’ve seen and heard several bears in the area exhibiting behaviors that lead us to ask, is this the breeding season for Andean bears in the dry forest? If so, has Chris sired cubs? What determines whether one male sires cubs and another male does not? We can generate hypotheses to address these questions, but it will take a lot more work and data to test the predictions of these hypotheses and reach conclusions about the answers to our questions.

After we finished our physical examination of Chris, we moved him to a comfortable, safe place to recover. The last we saw of him, he climbed up a 10-foot-tall (3 meters) rock face and slowly walks uphill, out of sight into the dry forest. Forty-eight hours later, according to data transmitted by his new GPS collar, he’s 2.72 miles (4.38 kilometers) away, in an area with plenty of sapote trees, which produce fruits that bears in this area often eat. We, on the other hand, have moved less than 100 yards (91 meters), because we’re continuing to try to collar more dry forest bears. I wonder if the next one will smell like Chris?